Vehicle cooling systems may include various cooling components such as radiators, cooling fans and blowers, condensers, liquid coolant, etc. An electro-drive engine cooling fan may be powered by an electric motor that is either variable speed or relay controlled. An electric fan controlled by a variable speed motor may be diagnosed by smart controllers connected to the powertrain control module (PCM).
Another example approach is shown by Wiltsch (US 2001/0199036) where a cooling fan is diagnosed by measuring current after the fan is triggered by a predefined signal. A current measuring device is coupled to a fan which can be triggered “on”, “off” or to an intermediate position. The device detects a current signal after the fan is triggered which is then compared with a predefined threshold. Any deviation from the predefined threshold results in a determination of a degraded fan.
The inventors herein have identified potential issues with the above approaches. In the example of a relay controlled fan, there is limited diagnostic capability due to the lack of smart controllers. This problem is particularly exacerbated for a fan system with multiple speeds which include several relays. Likewise, with regard to the current measurement approach, errors can be introduced in the vehicle electrical system due to the presence of other electrical loads that may be drawing current from the same voltage source as the fan, and unexpected or unknown transitions in such loads. Thus, interference from such electrical loads can result in erroneous current measurements for the fan and, consequently, lead to an incorrect diagnosis regarding cooling fan degradation.
The inventors herein have recognized the above issue and identified an approach to at least partly address the issue. In one example approach, a diagnostic method for a multiple speed, relay controlled fan system is provided. The method comprises measuring the change in current drawn from a battery-alternator system as fan speeds are varied during vehicle travel at lower speeds while other electrical loads are maintained in a more stable condition. Further, the difference between current drawn before and after a fan speed modification is compared with an expected change and a degradation is indicated if the absolute of a relative current change is more than an expected error threshold.
For example, while the vehicle is traveling at low speeds and larger electric loads like an air conditioner or defogger are in a stable condition, a fan diagnostic may be enabled. The PCM may command a change in fan speed and once the speed is stabilized, multiple current draw readings are acquired. For example, the fan speed may be changed from a stop or “off” position to a “low” speed state. Prior to changing the speed, the current drawn from the battery and alternator when the fan system is at an “off” position may be measured. Once the fan speed at “low” speed position has stabilized, the current drawn from the battery-alternator system may be measured. The difference between current drawn at an “off” position and current drawn at “low” speed may be calculated and compared with an expected difference to arrive at a relative error based on an expected change. If the absolute error calculated is more than an expected threshold, fan degradation may be detected. A malfunction indicator lamp may be lit on the dashboard after multiple degradation detections.
In this way, a multiple speed cooling fan system operated by relay controlled motors can be examined for degradation without any additional changes to existing hardware or the need for extra sensors, thereby, minimizing costs. By carrying out the diagnosis when other electrical loads are under more stable conditions, or by delaying requested changes in the other electrical loads, any change in current drawn from the battery-alternator system can be ascribed to the cooling fan system. Further, the cooling fan diagnostic may be disabled when other electric loads are fluctuating to minimize noise and errors.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.